18881021 has 2 divisors, whose sum is σ = 18881022. Its totient is φ = 18881020.

The previous prime is 18881017. The next prime is 18881039. The reversal of 18881021 is 12018881.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 511225 = 4286^2 + 715^2 .

It is a cyclic number.

It is not a de Polignac number, because 18881021 - 2² = 18881017 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18881011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9440510 + 9440511.

It is an arithmetic number, because the mean of its divisors is an integer number (9440511).

Almost surely, 2^18881021 is an apocalyptic number.

It is an amenable number.

18881021 is a deficient number, since it is larger than the sum of its proper divisors (1).

18881021 is an equidigital number, since it uses as much as digits as its factorization.

18881021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1024, while the sum is 29.

The square root of 18881021 is about 4345.2296832273. The cubic root of 18881021 is about 266.2820091267.

The spelling of 18881021 in words is "eighteen million, eight hundred eighty-one thousand, twenty-one".